Medical image processing system

ABSTRACT

Provided is a medical image processing system that can stably control the light emission amount of narrow-band light of a short wavelength in a case where the narrow-band light of the short wavelength is used for illumination of an observation target. A light source circuit emits specific narrow-band light of a short wavelength. An image sensor includes a first pixel group including a B pixel and a second pixel group including a G pixel. The B pixel has a higher sensitivity to the specific narrow-band light than the G pixel. The G pixel has a sensitivity to light in a green band and the specific narrow-band light. The light source control unit controls the light emission amount of the specific narrow-band light on the basis of a pixel value of the B pixel and a pixel value of the G pixel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2019/015757 filed on Apr. 11, 2019, which claims priority under 35U.S.C § 119(a) to Japanese Patent Application No. 2018-082158 filed onApr. 23, 2018. Each of the above application(s) is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a medical image processing system thatcontrols the light emission amount of narrow-band light of a shortwavelength used for illuminating an observation target.

2. Description of the Related Art

In the medical field, an endoscope system comprising a light sourcedevice, an endoscope, and a processor device is widely used. In theendoscope system, an observation target is irradiated with illuminationlight from the endoscope, and an image of the observation target isdisplayed on the monitor on the basis of an RGB image signal obtained byimaging the observation target illuminated with the illumination lightwith an image sensor of the endoscope.

Further, in diagnosis using an endoscope, since the brightness of theobservation target changes as a distance between a distal end portion ofthe endoscope having the image sensor and the observation targetchanges, the light emission amount of illumination light is controlledaccording to a change in brightness information of the observationtarget. In the case of using light in a plurality of red bands (540 nm,600 nm, and 630 nm) as illumination light in order to observe a bloodvessel at a deep position in a mucosal tissue, the brightnessinformation (dimming reference signal) of the observation targetcorresponding to the light in the plurality of red bands is calculatedto control the light emission amount of the illumination light (seeWO2013/145410A).

SUMMARY OF THE INVENTION

In endoscopic diagnosis in recent years, in order to observe specificstructures such as surface blood vessels and red blood cells,narrow-band light of a short wavelength having a center wavelength of410 nm to 450 nm is being used for illumination of an observationtarget. Also in a case of using such an observation target illuminatedwith narrow-band light of a short wavelength, it is required toaccurately calculate the brightness information of the observationtarget and to stably control the light emission amount of thenarrow-band light of the short wavelength.

An object of the invention is to provide a medical image processingsystem that can stably control the light emission amount of narrow-bandlight of a short wavelength in a case where the narrow-band light of theshort wavelength is used for illumination of an observation target.

A medical image processing system according to an aspect of theinvention comprises a light source unit that emits specific narrow-bandlight of a short wavelength, an image sensor that images an observationtarget illuminated with the specific narrow-band light, the image sensorincluding a first pixel group including a first pixel and a second pixelgroup including at least a second pixel, and a light source control unitthat controls a light emission amount of the specific narrow-band light.The first pixel has a higher sensitivity to the specific narrow-bandlight than the second pixel, the second pixel has a sensitivity to firstlong-wavelength light of a longer wavelength than the specificnarrow-band light and the specific narrow-band light, and the lightsource control unit controls the light emission amount of the specificnarrow-band light on the basis of a pixel value of the first pixelobtained in the first pixel and a pixel value of the second pixelobtained in the second pixel.

It is preferable that the second pixel group includes a third pixelhaving a sensitivity to broadband illumination light including thespecific narrow-band light and the first long-wavelength light, and thelight source control unit controls the light emission amount of thespecific narrow-band light on the basis of a pixel value of the thirdpixel in addition to the pixel value of the first pixel and the pixelvalue of the second pixel. It is preferable that the second pixel groupincludes a fourth pixel having a sensitivity to second long-wavelengthlight of a longer wavelength than the first long-wavelength light andthe specific narrow-band light, and the light source control unitcontrols the light emission amount of the specific narrow-band light onthe basis of a pixel value of the fourth pixel in addition to the pixelvalue of the first pixel and the pixel value of the second pixel.

It is preferable that the medical image processing system furthercomprises a brightness information calculation unit that calculatesbrightness information indicating brightness of the observation targeton the basis of the pixel value of the first pixel multiplied by abrightness adjustment coefficient for the first pixel and the pixelvalue of the second pixel multiplied by a brightness adjustmentcoefficient for the second pixel, the light source control unit controlsthe light emission amount of the specific narrow-band light on the basisof the brightness information, and a ratio between the brightnessadjustment coefficient for the first pixel and the brightness adjustmentcoefficient for the second pixel is determined on the basis of ashort-wavelength sensitivity to short-wavelength light including thespecific narrow-band light in the sensitivity of the first pixel and theshort-wavelength sensitivity of the second pixel.

It is preferable that the short-wavelength sensitivity of the secondpixel is 10% or more of a maximum sensitivity of the second pixel, or10% or more of the short-wavelength sensitivity of the first pixel. Itis preferable that the short-wavelength sensitivity of the second pixelis 35% or less of a maximum sensitivity of the second pixel, or 35% orless of the short-wavelength sensitivity of the first pixel.

It is preferable that the medical image processing system furthercomprises a brightness information calculation unit that calculatesbrightness information indicating brightness of the observation targeton the basis of the pixel value of the first pixel multiplied by abrightness adjustment coefficient for the first pixel, the pixel valueof the second pixel multiplied by a brightness adjustment coefficientfor the second pixel, and the pixel value of the third pixel multipliedby a brightness adjustment coefficient for the third pixel, the lightsource control unit controls the light emission amount of the specificnarrow-band light on the basis of the brightness information, and aratio between the brightness adjustment coefficient for the first pixel,the brightness adjustment coefficient for the second pixel, and thebrightness adjustment coefficient for the third pixel is determined onthe basis of a short-wavelength sensitivity to short-wavelength lightincluding the specific narrow-band light in the sensitivity of the firstpixel, the short-wavelength sensitivity of the second pixel, and theshort-wavelength sensitivity of the third pixel.

It is preferable that the medical image processing system furthercomprises a brightness information calculation unit that calculatesbrightness information indicating brightness of the observation targeton the basis of the pixel value of the first pixel multiplied by abrightness adjustment coefficient for the first pixel, the pixel valueof the second pixel multiplied by a brightness adjustment coefficientfor the second pixel, and the pixel value of the fourth pixel multipliedby a brightness adjustment coefficient for the fourth pixel, the lightsource control unit controls the light emission amount of the specificnarrow-band light on the basis of the brightness information, and aratio between the brightness adjustment coefficient for the first pixel,the brightness adjustment coefficient for the second pixel, and thebrightness adjustment coefficient for the fourth pixel is determined onthe basis of a short-wavelength sensitivity to short-wavelength lightincluding the specific narrow-band light in the sensitivity of the firstpixel, the short-wavelength sensitivity of the second pixel, and theshort-wavelength sensitivity of the fourth pixel.

It is preferable that the number of pixels of the second pixel group isgreater than the number of pixels of the first pixel group. It ispreferable that a center wavelength of the specific narrow-band light isincluded in a range of 400 nm to 450 nm, and a half-width of thespecific narrow-band light is 40 nm or less.

According to the invention, it is possible to stably control the lightemission amount of narrow-band light of a short wavelength in a casewhere the narrow-band light of the short wavelength is used forillumination of an observation target.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of an endoscope system.

FIG. 2 is a block diagram showing a function of the endoscope system.

FIG. 3 is a graph showing spectra of violet light V, blue light B, greenlight G, and red light R.

FIG. 4 is a graph showing a spectrum of specific narrow-band light of ashort wavelength.

FIG. 5 is an explanatory diagram showing R pixels (R), G pixels (G), Bpixels (B), and W pixels (W) provided in an image sensor.

FIG. 6 is a graph showing spectral transmittances of a B filter, a Gfilter, and an R filter included in an image sensor of the presentembodiment.

FIG. 7 is an explanatory diagram showing received light intensities of aB pixel and a G pixel in a case where an esophagus is illuminated withspecific narrow-band light of a short wavelength.

FIG. 8 is an explanatory diagram showing received light intensities of aB pixel and an R pixel in a case where an esophagus is illuminated withspecific narrow-band light of a short wavelength.

FIG. 9 is an explanatory diagram showing received light intensities of aW pixel and a G pixel in a case where an observation target isilluminated with normal light.

FIG. 10 is an explanatory diagram showing received light intensities ofa W pixel and an R pixel in a case where an esophagus is illuminatedwith normal light.

FIG. 11 is an explanatory diagram showing a G pixel located at aspecific position SP in an image signal.

FIG. 12 is an explanatory diagram showing a method of calculating a lowfrequency component mW.

FIG. 13 is an explanatory diagram showing a method of calculating a lowfrequency component mBx.

FIG. 14 is an explanatory diagram showing a method of calculating a lowfrequency component mBy.

FIG. 15 is an explanatory diagram showing an image sensor having a Bayerarray.

FIG. 16 is an explanatory diagram used for describing a method ofcalculating a pixel value of a B pixel at a G pixel position in theimage sensor having a Bayer array.

FIG. 17 is an explanatory diagram used for describing a method ofcalculating a pixel value of a B pixel at an R pixel position in theimage sensor having a Bayer array.

FIG. 18 is a graph showing spectral transmittances of a B filter, a Gfilter, and an R filter included in a normal image sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

As shown in FIG. 1 , an endoscope system 10 according to a firstembodiment has an endoscope 12, a light source device 14, a processordevice 16, a monitor 18, and a user interface 19. The endoscope 12 isoptically connected to the light source device 14 and electricallyconnected to the processor device 16. The endoscope 12 has an insertionpart 12 a to be inserted into a subject, an operation part 12 b providedin a proximal end portion of the insertion part 12 a, and a bendableportion 12 c and a distal end portion 12 d that are provided on thedistal end side of the insertion part 12 a. The bendable portion 12 c isbent by operating an angle knob 12 e of the operation part 12 b. Withthe bending operation, the distal end portion 12 d is directed in adesired direction. The user interface 19 includes a mouse or the like inaddition to the illustrated keyboard.

In addition to the angle knob 12 e, a mode switching SW 13 a and a stillimage acquisition instruction part 13 b are provided in the operationpart 12 b. The mode switching SW 13 a is used to switch among a normalobservation mode, a special observation mode, and a short wavelengthobservation mode. The normal observation mode is a mode in which anobservation target is illuminated with normal light such as white light(see FIGS. 9 and 10 ) and a normal image is displayed on the monitor 18.The special observation mode is a mode in which an observation target isilluminated with special light such as blue narrow-band light, and aspecial observation image in which a structure such as a blood vessel ata specific depth is emphasized is displayed on the monitor 18. The shortwavelength observation mode is a mode in which a short wavelengthobservation image showing a structure that can be observed with specificnarrow-band light of a short wavelength (corresponding to violet light Vdescribed later) is displayed on the monitor 18 by using the specificnarrow-band light of the short wavelength for illumination of anobservation target. As the mode switching unit for switching the mode, afoot switch may be used in addition to the mode switching SW 13 a.

The processor device 16 is electrically connected to the monitor 18 andthe user interface 19. The monitor 18 outputs and displays imageinformation and the like. The user interface 19 functions as a userinterface (UI) that receives input operations such as function settings.An external recording unit (not shown) for recording image informationand the like may be connected to the processor device 16.

As shown in FIG. 2 , the light source device 14 has a light source unit20, a light source control unit 21, and an optical path coupling unit23. The light source unit 20 has a violet light emitting diode (V-LED)20 a, a blue light emitting diode (B-LED) 20 b, a green light emittingdiode (G-LED) 20 c, and a red light emitting diode (R-LED) 20 d. Thelight source control unit 21 controls driving of the LEDs 20 a to 20 d.The optical path coupling unit 23 couples optical paths of light of fourcolors emitted from the LEDs 20 a to 20 d of four colors. The lightcoupled by the optical path coupling unit 23 is emitted into the subjectthrough a light guide 41 and an illumination lens 45 which are insertedinto the insertion part 12 a. A laser diode (LD) may be used instead ofthe LED.

As shown in FIG. 3 , the V-LED 20 a generates violet light V having acenter wavelength of 400 nm to 450 nm (for example, 405 nm) and ahalf-width of 40 nm or less. The B-LED 20 b generates blue light Bhaving a center wavelength of 450 nm to 500 nm (for example, 460 nm) anda half-width of 40 nm or less. The G-LED 20 c generates green light Ghaving a wavelength range of 480 nm to 600 nm. The R-LED 20 d generatesred light R having a center wavelength of 620 nm to 630 nm and awavelength range of 600 nm to 650 nm.

The light source control unit 21 performs control to turn on the V-LED20 a, the B-LED 20 b, the G-LED 20 c, and the R-LED 20 d in the normalobservation mode and the special observation mode. In the normalobservation mode, the light source control unit 21 controls each of theLEDs 20 a to 20 d so as to emit normal light in which a light intensityratio among the violet light V, the blue light B, the green light G, andthe red light R is Vc:Bc:Gc:Rc. In the special observation mode, thelight source control unit 21 controls each of the LEDs 20 a to 20 d soas to emit special light in which the light intensity ratio among theviolet light V, the blue light B, the green light G, and the red light Ris Vs:Bs:Gs:Rs. It is preferable that the special light can emphasize astructure such as a blood vessel at a specific depth. Further, as shownin FIG. 4 , in the short wavelength observation mode, the light sourcecontrol unit 21 controls each of the LEDs 20 a to 20 d so as to emit theviolet light V which is the specific narrow-band light of the shortwavelength.

In the present specification, the light intensity ratio includes a casewhere the ratio of at least one semiconductor light source is 0 (zero).Accordingly, a case where any one or two or more of the semiconductorlight sources are not turned on is included. For example, as in the casewhere the light intensity ratio among the violet light V, the blue lightB, the green light G, and the red light R is 1:0:0:0, even in a casewhere only one of the semiconductor light sources is turned on and theother three are not turned on, it is assumed that a light intensityratio is present.

Further, the light source control unit 21 controls the light emissionamount of the illumination light emitted from each of the LEDs 20 a to20 d on the basis of brightness information sent from a brightnessinformation calculation unit 54 of the processor device 16. In the caseof the normal observation mode, the light source control unit 21controls the light emission amount of the normal light so as to satisfythe following Equation A) on the basis of brightness information for thenormal observation mode. For example, in a case where “brightnessinformation for normal observation mode/256” is lower than a specifiednumber, control is performed to increase the light emission amount ofthe normal light. In contrast, in a case where “brightness informationfor normal observation mode/256” is higher than a specified number,control is performed to reduce the light emission amount of the normallight.Brightness information for normal observation mode/256=specifiednumber  Equation A)

In the case of the special observation mode, the light source controlunit 21 controls the light emission amount of the special light so as tosatisfy the following Equation B) on the basis of brightness informationfor the special observation mode. For example, in a case where“(brightness information for special observation mode+additioncoefficient for special observation mode)/256” is lower than a specifiednumber, control is performed to increase the light emission amount ofthe special light. In contrast, in a case where “(brightness informationfor special observation mode+addition coefficient for specialobservation mode)/256” is higher than a specified number, control isperformed to reduce the light emission amount of the special light.(Brightness information for special observation mode+additioncoefficient for special observation mode)/256=specified number  EquationB)

In the case of the short wavelength observation mode, the light sourcecontrol unit 21 controls the light emission amount of the specificnarrow-band light of the short wavelength so as to satisfy the followingEquation C) on the basis of brightness information for the shortwavelength observation mode. For example, in a case where “(brightnessinformation for short wavelength observation mode+addition coefficientfor short wavelength observation mode)/256” is lower than a specifiednumber, control is performed to increase the light emission amount ofthe specific narrow-band light of the short wavelength. In contrast, ina case where “(brightness information for short wavelength observationmode+addition coefficient for short wavelength observation mode)/256” ishigher than a specified number, control is performed to reduce the lightemission amount of the specific narrow-band light of the shortwavelength.(Brightness information for short wavelength observation mode+additioncoefficient for short wavelength observation mode)/256=specifiednumber  Equation C)

The brightness information for the short wavelength observation mode iscalculated by including a G image signal having a signal valuecorresponding to the specific narrow-band light in addition to a B imagesignal, and thus it is possible to stably control the light emissionamount of the specific narrow-band light. For example, in a case where ablue-related dye is scattered on the observation target, when thebrightness information for the short wavelength observation mode iscalculated on the basis of only the B image signal, it is difficult tostably control the light emission amount of the specific narrow-bandlight of the short wavelength. As in the present embodiment, thebrightness information for the short wavelength observation mode iscalculated on the basis of the G image signal in addition to the B imagesignal, so that it is less likely to be affected by the blue-relateddye. Therefore, it is possible to stably control the light emissionamount of the specific narrow-band light of the short wavelength.

Also in a case where the brightness information for the short wavelengthobservation mode is calculated on the basis of the B image signal, the Gimage signal, and a W image signal, the W image signal is less likely tobe affected by the blue-related dye. Therefore, the light emissionamount of the specific narrow-band light can be stably controlledaccording to the brightness information based on the B image signal, theG image signal, and the W image signal. Similarly, also in a case wherethe brightness information for the short wavelength observation mode iscalculated on the basis of the B image signal, the G image signal, andan R image signal, the R image signal is less likely to be affected bythe blue-related dye. Therefore, the light emission amount of thespecific narrow-band light can be stably controlled according to thebrightness information based on the B image signal, the G image signal,and the R image signal.

As shown in FIG. 2 , the light guide 41 is built in the endoscope 12 anda universal cord (a cord that connects the endoscope 12 to the lightsource device 14 and the processor device 16), and propagates the lightcoupled by the optical path coupling unit 23 to the distal end portion12 d of the endoscope 12. It is possible to use a multi-mode fiber asthe light guide 41. As an example, it is possible to use asmall-diameter fiber cable of which a core diameter is 105 μm, acladding diameter is 125 μm, and a diameter including a protective layeras an outer skin is φ0.3 mm to φ0.5 mm.

An illumination optical system 30 a and an imaging optical system 30 bare provided in the distal end portion 12 d of the endoscope 12. Theillumination optical system 30 a has the illumination lens 45, and theobservation target is irradiated with the light from the light guide 41through the illumination lens 45. The imaging optical system 30 b has anobjective lens 46 and an image sensor 48. The reflected light from theobservation target is incident on the image sensor 48 through theobjective lens 46. In this manner, a reflected image of the observationtarget is formed on the image sensor 48.

The image sensor 48 is a color image sensor and captures a reflectedimage of the subject to output an image signal. The image sensor 48 ispreferably a charge coupled device (CCD) image sensor, a complementarymetal-oxide semiconductor (CMOS) image sensor, or the like. The imagesensor 48 used in the invention is a color image sensor for obtainingRGBW image signals of four colors of red (R), green (G), blue (B), andwhite (W). That is, as shown in FIG. 5 , the image sensor 48 comprisesan R pixel (fourth pixel) provided with an R filter, a G pixel (secondpixel) provided with a G filter, a B pixel (first pixel) provided with aB filter, and a W pixel (third pixel) provided with a W filter. Theimage sensor 48 is divided into two pixel groups of a first pixel groupand a second pixel group, and the number of pixels of the second pixelgroup is greater than the number of pixels of the first pixel group. Thefirst pixel group includes B pixels, and the second pixel group includesG pixels, R pixels, and W pixels.

In the image sensor 48, the W pixels are arranged in a checkeredpattern. Further, for the signal obtained by the image sensor 48 in theshort wavelength observation mode, in order to improve the resolution,as shown in demosaicing processing described later, by giving the Gpixel a certain level or more of a sensitivity to the specificnarrow-band light and using the correlation between the W pixel and theG pixel, a signal of the specific narrow-band light can be obtained evenat a G pixel position. Similarly, by giving the R pixel a certain levelor more of a sensitivity to the specific narrow-band light and using acorrelation between the W pixel and the R pixel, a signal of thespecific narrow-band light can be obtained even at an R pixel position.

As described above, in order to obtain a signal of specific narrow-bandlight at the G pixel position during illumination with specificnarrow-band light of a short wavelength, as shown in FIG. 6 , thetransmittance of the G filter is set so that the G pixel has not onlythe sensitivity to light in a green band (first long-wavelength light)of 500 nm to 600 nm, but also the short-wavelength sensitivity toshort-wavelength light (a wavelength band is 450 nm or less, forexample, 400 nm to 450 nm) including the specific narrow-band light ofthe short wavelength. In this manner, as shown in FIG. 7 , in a casewhere the specific narrow-band light, the transmittance of the G filter,and the reflectance of each part (the reflectance of the “esophagus” isused in the case of FIG. 7 , and the reflectances of the stomach andlarge intestine are shown by the dotted line) are multiplied, a receivedlight intensity corresponding to the wavelength range of the specificnarrow-band light is obtained as a received light intensity of the Gpixel. A received light intensity of the B pixel is obtained bymultiplying the specific narrow-band light, the transmittance of the Bfilter (blue band of 400 nm to 500 nm), and the reflectance of eachpart, and is a constant multiple of the intensity value of the receivedlight intensity of the G pixel.

In a case where the signal value obtained by the G pixel is small, theinfluence of noise increases, and the image quality of the image afterthe demosaicing processing deteriorates. Therefore, for example, ashort-wavelength sensitivity of the G pixel is preferably 10% or more ofthe maximum sensitivity of the G pixel at 400 nm to 450 nm. That is, inthe G filter, the transmittance at 400 nm to 450 nm is preferably 10% ormore of the transmittance at the wavelength range (for example, 540 nmto 560 nm) corresponding to the maximum sensitivity of the G pixel.Alternatively, the short-wavelength sensitivity of the G pixel ispreferably 10% or more of a short-wavelength sensitivity of the B pixel.That is, in the G filter, the transmittance at 400 nm to 450 nm ispreferably 10% or more of the transmittance at 400 nm to 450 nm of the Bfilter. The maximum sensitivity of the G pixel refers to the sensitivityto light in the wavelength range in which the transmittance of the Gcolor filter is equal to or higher than a certain value (for example,70%). The same applies to the maximum sensitivity of the R pixel.

On the other hand, in a case where the short-wavelength sensitivity ofthe G pixel becomes too high, the color reproducibility in a normalimage deteriorates. Therefore, the short-wavelength sensitivity of the Gpixel is preferably 35% or less of the maximum sensitivity of the Gpixel at 400 nm to 450 nm. That is, in the G filter, the transmittanceat 400 nm to 450 nm is preferably 35% or less of the transmittance atthe wavelength range (for example, 540 nm to 560 nm) corresponding tothe maximum sensitivity of the G pixel. Alternatively, theshort-wavelength sensitivity of the G pixel is preferably 35% or less ofthe short-wavelength sensitivity of the B pixel. That is, in the Gfilter, the transmittance at 400 nm to 450 nm is preferably 35% or lessof the transmittance at 400 nm to 450 nm of the B filter.

Further, in order to obtain a signal of specific narrow-band light atthe R pixel position during illumination with specific narrow-band lightof a short wavelength, as shown in FIG. 6 , the transmittance of the Rfilter is set so that the R pixel has not only the sensitivity to lightin a red band (second long-wavelength light) of 600 nm to 700 nm, butalso the short-wavelength sensitivity to short-wavelength light (400 nmto 450 nm) including the specific narrow-band light of the shortwavelength. In this manner, as shown in FIG. 8 , in a case where thespecific narrow-band light, the transmittance of the R filter, and thereflectance of each part (the reflectance of the “esophagus” is used inthe case of FIG. 8 , and the reflectances of the stomach and largeintestine are shown by the dotted line) are multiplied, a received lightintensity corresponding to the wavelength range of the specificnarrow-band light is obtained as a received light intensity of the Rpixel. The received light intensity of the B pixel is a constantmultiple of the received light intensity of the R pixel.

Here, in a case where the signal value obtained by the R pixel is small,the influence of noise increases, and the image quality of the imageafter the demosaicing processing deteriorates. Therefore, for example, ashort-wavelength sensitivity of the R pixel is preferably 10% or more ofthe maximum sensitivity of the R pixel at 400 nm to 450 nm. That is, inthe R filter, the transmittance at 400 nm to 450 nm is preferably 10% ormore of the transmittance at the wavelength range (for example, 640 nmto 660 nm) corresponding to the maximum sensitivity of the R pixel.Alternatively, the short-wavelength sensitivity of the R pixel ispreferably 10% or more of the short-wavelength sensitivity of the Bpixel. That is, in the R filter, the transmittance at 400 nm to 450 nmis preferably 10% or more of the transmittance at 400 nm to 450 nm ofthe B filter.

On the other hand, in a case where the short-wavelength sensitivity ofthe R pixel becomes too high, the color reproducibility in a normalimage deteriorates. Therefore, the short-wavelength sensitivity of the Rpixel is preferably 35% or less of the maximum sensitivity of the Rpixel at 400 nm to 450 nm. That is, in the R filter, the transmittanceat 400 nm to 450 nm is preferably 35% or less of the transmittance atthe wavelength range (for example, 640 nm to 660 nm) corresponding tothe maximum sensitivity of the R pixel. Alternatively, theshort-wavelength sensitivity of the R pixel is preferably 35% or less ofthe short-wavelength sensitivity of the B pixel. That is, in the Rfilter, the transmittance at 400 nm to 450 nm is preferably 35% or lessof the transmittance at 400 nm to 450 nm of the B filter.

In the image sensor 48, since the W pixel has a spectral sensitivity tothe illumination light of the broadband light from the blue band to thered band so that the W pixel includes the specific narrow-band light ofthe short wavelength, the light in the green band, and the light in thered band, the saturation of the pixel value is faster than other pixelssuch as the B pixel, the G pixel, and the R pixel. Accordingly, thesensitivity of the W pixel is set lower than the sensitivity of otherpixels such as the B pixel, the G pixel, and the R pixel. Specifically,the sensitivity of the W pixel is preferably 30% to 50% with respect tothe maximum sensitivity of the B pixel (for example, a sensitivity at440 nm to 460 nm) or the maximum sensitivity of the G pixel (forexample, a sensitivity at 540 nm to 560 nm).

For example, in the relationship regarding the sensitivity between the Wpixel and the G pixel, as shown in FIG. 9 , the transmittance of the Wfilter is set so that a received light intensity of the W pixel obtainedby multiplying the light source spectrum of the normal light and thetransmittance of the W filter is about 50% (for example, 45% to 55%) ofthe received light intensity of the G pixel obtained by multiplying thelight source spectrum of normal light and the transmittance of the Gfilter. Alternatively, in the relationship regarding the sensitivitybetween the W pixel and the B pixel, as shown in FIG. 10 , thetransmittance of the W filter is set so that the received lightintensity of the W pixel obtained by multiplying the light sourcespectrum of the normal light and the transmittance of the W filter isabout 50% (for example, 45% to 55%) of the received light intensity ofthe B pixel obtained by multiplying the light source spectrum of normallight, the transmittance of the B filter, and the reflectance of theesophagus.

The image sensor 48 may be a so-called complementary color image sensorcomprising complementary color filters of cyan (C), magenta (M), yellow(Y), and green (G) instead of the RGBW color image sensor. In a case ofusing the complementary color image sensor, since four color imagesignals of CMYG are output, it is necessary to convert the four colorimage signals of CMYG into three color image signals of RGB bycomplementary color-primary color conversion. The image sensor 48 may bea monochrome image sensor without a color filter.

As shown in FIG. 2 , the image signal output from the image sensor 48 istransmitted to a CDS/AGC circuit 50. The CDS/AGC circuit 50 performscorrelated double sampling (CDS) and auto gain control (AGC) on an imagesignal which is an analog signal. The image signal that has passedthrough the CDS/AGC circuit 50 is converted into a digital image signalby an analog/digital (A/D) converter 52. The A/D converted digital imagesignal is input to the processor device 16.

The processor device 16 comprises an image acquisition unit 53, thebrightness information calculation unit 54, a digital signal processor(DSP) 56, a noise removal unit 58, an image processing unit 60, aparameter switching unit 62, and a display control unit 64.

The image acquisition unit 53 acquires an observation image obtained byimaging the observation target with the endoscope 12. Specifically, adigital color image signal from the endoscope 12 is input to the imageacquisition unit 53 as an observation image. The color image signal isan RGBW image signal composed of an R image signal (a pixel value of anR pixel) output from the R pixel of the image sensor 48, a G imagesignal (a pixel value of a G pixel) output from the G pixel of the imagesensor 48, a B image signal (a pixel value of a B pixel) output from theB pixel of the image sensor 48, and a W image signal (a pixel value of aW pixel) output from the W pixel of the image sensor 48.

The brightness information calculation unit 54 calculates brightnessinformation indicating the brightness of the observation target for eachobservation mode on the basis of the RGBW image signal input from theimage acquisition unit 53. The calculated brightness information is sentto the light source control unit 21 and is used to control the lightemission amount of the illumination light. The brightness information isrepresented by, for example, the number of bits.

In the case of the normal observation mode, the brightness informationfor the normal observation mode is calculated by the following EquationK).Brightness information for normal observation mode=brightness adjustmentcoefficient kcr×R image signal+brightness adjustment coefficient kcg×Gimage signal+brightness adjustment coefficient kcb×B imagesignal+brightness adjustment coefficient kcw×W image signal  Equation K)

In the case of the special observation mode, the brightness informationfor the special observation mode is calculated by the following EquationL).Brightness information for special observation mode=brightnessadjustment coefficient ksr×R image signal+brightness adjustmentcoefficient ksg×G image signal+brightness adjustment coefficient ksb×Bimage signal+brightness adjustment coefficient ksw×W imagesignal  Equation L)

In the case of the short wavelength observation mode, the brightnessinformation for the short wavelength observation mode is calculated bythe following Equation M).Brightness information for short wavelength observation mode=brightnessadjustment coefficient ktr×R image signal+brightness adjustmentcoefficient ktg×G image signal+brightness adjustment coefficient ktb×Bimage signal+brightness adjustment coefficient ktw×W imagesignal  Equation M)

Since only the specific narrow-band light of the short wavelength isilluminated in the short wavelength observation mode, in the calculationof the brightness information for the short wavelength observation mode,only the B image signal and the W image signal having the pixel valuecorresponding to the specific narrow-band light of the short wavelengthmay be used. However, in the present embodiment, since the G pixel andthe R pixel have the short-wavelength sensitivity, the G image signaland the R image signal are also used together in the calculation of thebrightness information for the short wavelength observation mode.

In order to accurately calculate the brightness information for theshort wavelength observation mode that corresponds to the illuminationof only the specific narrow-band light of the short wavelength, it ispreferable that the ratio between the brightness adjustment coefficientktr (brightness adjustment coefficient for the fourth pixel), thebrightness adjustment coefficient ktg (brightness adjustment coefficientfor the second pixel), the brightness adjustment coefficient ktb(brightness adjustment coefficient for the first pixel), and thebrightness adjustment coefficient ktw (brightness adjustment coefficientfor the third pixel) is determined on the basis of the short-wavelengthsensitivity of the R pixel, the G pixel, the B pixel, and the W pixeland the reflectance of the mucous membrane.

Here, in a case where Equation M) is used, when the spectral sensitivityof the W pixel is about 45% of the spectral sensitivity of the B pixelat 400 nm to 420 nm, and 15% to 20% of the spectral sensitivity of the Gpixel and the R pixel at 400 nm to 420 nm, in consideration of thereflectance of the mucous membrane, it is preferable that the ratiobetween the brightness adjustment coefficient ktr, the brightnessadjustment coefficient ktg, the brightness adjustment coefficient ktb,and the brightness adjustment coefficient ktw is set to “2:2:5:4”.

The brightness information for the short wavelength observation mode ispreferably calculated on the basis of at least two image signals of theB image signal and the G image signal. In a case where the brightnessinformation for the short wavelength observation mode is calculated onthe basis of the B image signal and the G image signal, the calculationis performed by Equation M1).Brightness information for short wavelength observation mode=brightnessadjustment coefficient ktg×G image signal+brightness adjustmentcoefficient ktb×B image signal  Equation M1)

Here, in a case where Equation M1) is used, when the spectralsensitivity of the G pixel at 400 nm to 420 nm is 15% to 20% of thespectral sensitivity of the B pixel at 400 nm to 420 nm, inconsideration of the reflectance of the mucous membrane, it ispreferable that the ratio between the brightness adjustment coefficientktg and the brightness adjustment coefficient ktb is set to “2:5”.

Further, in a case where the brightness information for the shortwavelength observation mode is calculated on the basis of the B imagesignal, the G image signal, and the W image signal, the calculation isperformed by Equation M2).Brightness information for short wavelength observation mode=brightnessadjustment coefficient ktg×G image signal+brightness adjustmentcoefficient ktb×B image signal+brightness adjustment coefficient ktw×Wimage signal  Equation M2)

Here, in a case where Equation M2) is used, when the spectralsensitivity of the W pixel is about 45% of the spectral sensitivity ofthe B pixel at 400 nm to 420 nm, in consideration of the reflectance ofthe mucous membrane, it is preferable that the ratio between thebrightness adjustment coefficient ktg, the brightness adjustmentcoefficient ktb, and the brightness adjustment coefficient ktw is set to“2:5:4”.

Further, in a case where the brightness information for the shortwavelength observation mode is calculated on the basis of the B imagesignal, the G image signal, and the R image signal, the calculation isperformed by Equation M3).Brightness information for short wavelength observation mode=brightnessadjustment coefficient ktr×R image signal+brightness adjustmentcoefficient ktg×G image signal+brightness adjustment coefficient ktb×Bimage signal  Equation M3)

Here, in a case where Equation M3) is used, when the spectralsensitivity of the G pixel and the R pixel at 400 nm to 420 nm is 15% to20% of the spectral sensitivity of the B pixel at 400 nm to 420 nm, inconsideration of the reflectance of the mucous membrane, it ispreferable that the ratio between the brightness adjustment coefficientktr, the brightness adjustment coefficient ktg, and the brightnessadjustment coefficient ktb is set to “2:2:5”.

The DSP 56 performs various kinds of signal processing, such as defectcorrection processing, offset processing, gain correction processing,linear matrix processing, or gamma conversion processing, on thereceived image signal. In the defect correction processing, a signal ofa defective pixel of the image sensor 48 is corrected. In the offsetprocessing, a dark current component is removed from the image signalsubjected to the defect correction processing, and an accurate zerolevel is set. In the gain correction processing, a signal level isadjusted by multiplying the image signal after the offset processing bya specific gain. The linear matrix processing for improving the colorreproducibility is performed on the image signal after the gaincorrection processing. After that, brightness and saturation areadjusted by the gamma conversion processing.

The demosaicing processing (also referred to as isotropic processing orsynchronization processing) is performed on the image signal after thelinear matrix processing in the demosaicing processing unit 56 a. In thenormal observation mode and the special observation mode, a signal ofthe color lacking in each pixel is generated by interpolation. By thedemosaicing processing, all pixels have signals of RGB colors. For thedemosaicing processing in a case where a color image sensor forobtaining an RGBW image signal is used, for example, the methoddisclosed in JP2011-055038A can be used.

In the short wavelength observation mode, the observation target isilluminated with only the specific narrow-band light of the shortwavelength. However, in a normal RGB image sensor (an image sensorconsisting of R pixels, G pixels, and B pixels), as shown in FIG. 18 ,the G filter and the R filter have almost no transmittance in thespecific narrow-band, and the G pixel and the R pixel have almost nosensitivity to the specific narrow-band light. Therefore, in the shortwavelength observation image obtained on the basis of the specificnarrow-band light of the short wavelength, signals are obtained onlyfrom the B pixel and the W pixel having a sensitivity to specificnarrow-band light, and almost no signals are obtained from the G pixeland the R pixel. For this reason, even if the demosaicing processingbased on the correlation with the W pixel is performed, a shortwavelength observation image with high resolution cannot be obtained.However, as shown in the present embodiment, by giving the G pixel andthe R pixel the sensitivity to the specific narrow-band light, aconstant signal corresponding to the specific narrow-band light can beobtained also from the G pixel and the R pixel, and therefore, a shortwavelength observation image with high resolution can be obtained by thedemosaicing processing based on the correlation with the W pixel. In thenormal RGB image sensor, the G filter and the R filter have almost notransmittance in the blue band as shown in FIG. 18 , so that the G pixeland the R pixel have almost no sensitivity in the blue band.

Hereinafter, in the short wavelength observation mode, by the signalsobtained from the B pixel and the W pixel and the demosaicing processingbased on the correlation with the W pixel, the signals obtained from theG pixel and the R pixel have a constant signal corresponding to thespecific narrow-band light, and therefore, each signal is referred to asa short wavelength observation signal.

The method of calculating the pixel value of B pixel at the G pixelposition as the short wavelength observation signal by the demosaicingprocessing based on the correlation with the pixel value of the W pixelis as follows. For example, as shown in FIG. 11 , in an image signal 80output from the image sensor 48, in a case of calculating a pixel valueBd of the B pixel at the G pixel position at a specific position SP, fordiscrete W pixel signals included in the image signal 80, W pixel valuesat all pixel positions are calculated by direction discriminationinterpolation according to the neighboring W pixel values, image blurreduction processing for reducing image blur is performed on thecalculated W pixel values by Wiener filter processing, and a W pixelsignal (=Wd) after the image blur reduction processing (an image blurreduction processed signal) is calculated. Next, as shown in FIG. 12 ,by multiplying the pixel values of a 5×5 pixel area (a specific pixelarea) by a first smoothing filter 82, a low frequency component mW (afirst smooth-filtered component) is obtained. The first smoothing filter82 is provided with a filter coefficient (such as “1” or “2”) at theposition where the W pixel is present in the image signal 80.

Next, as shown in FIG. 13 , by multiplying the pixel values of the 5×5pixel area by a second smoothing filter 84, a low frequency componentmBx (a second smooth-filtered component) is obtained. The secondsmoothing filter 84 is a filter that is applied to each 5×5 pixel areain which the G pixel is located at the specific position SP, and isprovided with a filter coefficient (such as “1”) at the position wherethe B pixel is present in the image signal 80. In the second smoothingfilter 84, the filter coefficient setting is performed so that the pixelvalues of the B pixels at positions close to the specific position SPare evenly acquired. Then, the pixel value Bd of the B pixel at the Gpixel position is calculated by the following Equation X).Bd=(mBx/mW)×Wd  Equation X)

The method of calculating the pixel value of B pixel at the R pixelposition as the short wavelength observation signal by the demosaicingprocessing based on the correlation with the pixel value of the W pixelis as follows. Similar to the above case, a blur correction white (W)signal (=Wd) and the low frequency component mW are acquired. Then, asshown in FIG. 14 , by multiplying the pixel values of the 5×5 pixel areaby a third smoothing filter 86, a low frequency component mBy (a thirdsmoothing filtered component) is acquired. The third smoothing filter 86is a filter that is applied to each 5×5 pixel area in which the R pixelis located at the specific position SP, and is provided with a filtercoefficient (such as “1”) at the position where the B pixel is presentin the image signal 80. Then, the pixel value Bd of the B pixel at the Rpixel position is calculated by the following Equation Y).Bd=(mBy/mW)×Wd  Equation Y)

The noise removal unit 58 removes noise from the RGB image signal byperforming noise removal processing (for example, a moving averagemethod or a median filter method) on the image signal that has beensubjected to gamma correction or the like by the DSP 56. The imagesignal from which the noise has been removed is transmitted to the imageprocessing unit 60.

The image processing unit 60 performs image processing corresponding toeach observation mode. As an image processing method, for example, thereis a method in which image processing parameters such as gradationprocessing and saturation enhancement corresponding to each observationmode are prepared, and the image signal is multiplied by the imageprocessing parameters according to each observation mode. In the case ofthe normal observation mode, the RGB image signal is multiplied by aparameter for the normal observation mode, and in the case of thespecial observation mode, the RGB image signal is multiplied by aparameter for the special observation mode. In the case of the shortwavelength observation mode, the B image signal is multiplied by aparameter for the short wavelength observation mode. The parameter forthe normal observation mode, the parameter for the special observationmode, and the parameter for the short wavelength observation modedescribed above are switched by the parameter switching unit 62 inaccordance with the mode switching of the mode switching SW 13 a.

The display control unit 64 performs control for displaying an imagesignal input from the image processing unit 60 as an image that can bedisplayed on the monitor 18. In the case of the normal observation mode,a normal image is displayed on the monitor 18 by assigning the R imagesignal to the R channel of the monitor 18, the G image signal to the Gchannel of the monitor 18, and the B image signal to the B channel ofthe monitor 18. In the case of the special observation mode, a specialobservation image is displayed on the monitor 18 by assigning the Gimage signal to the R channel of the monitor 18, and the B image signalto the G channel and the B channel of the monitor 18 (in assigning, itis preferable to perform gradation processing and saturationenhancement). On the other hand, in the case of the short wavelengthobservation mode, a short wavelength observation image is displayed onthe monitor 18 by assigning the short wavelength observation signal toeach of the R, G, and B channels of the monitor 18. In assigning theshort wavelength observation signal, the short wavelength observationimage is multiplied by a gain for each of the R, G, and B channels, andthe like, and then assigned to each channel. In this manner, the shortwavelength observation image showing a structure that can be observedwith specific narrow-band light of a short wavelength can be displayedon the monitor 18 as an image having a specific background color inwhich the structure of blood vessels and the like has better visibilitythan a gray image.

Second Embodiment

In the first embodiment, the RGBW image sensor is used as the imagesensor 48, but as shown in FIG. 15 , an image sensor having a Bayerarray in which the ratio between the number of pixels of G pixels, Bpixels, and R pixels is 2:1:1 may be used. In a case where the imagesensor having a Bayer array is used, as demosaicing processing in theshort wavelength observation mode for obtaining monochrome B imagesignals at all pixel positions, it is preferable to calculate a pixelvalue Bg of the B pixel at the G pixel position and a pixel value Br ofthe B pixel at the R pixel position as follows.

For example, as shown in FIG. 16 , in a case of calculating a pixelvalue Bg(22) of the B pixel at the pixel position of the G pixel (G22)at the specific position SP, the calculation is performed by EquationZ1).Bg(22)=G22×2(B21+B23)/(G11+G13+G31+G33)  Equation Z1)

According to Equation Z1), not only the pixel value of the B pixelaround the specific position SP but also the pixel value of the G pixelis used, so that a more realistic pixel value of Bg(22) can be obtained.

Note that, as shown in FIG. 17 , in a case of calculating a pixel valueBr(32) of the B pixel at the pixel position of the R pixel (R32) at thespecific position SP, the calculation is performed by Equation Z2).Br(32)=(B21+B23+B41+B43)/4  Equation Z2)

In the first and second embodiments, in the demosaicing processing inthe short wavelength observation mode, the pixel value (B image signal)of the B pixel at the G pixel position and the R pixel position iscalculated; however, similarly to the normal observation mode or thespecial observation mode, the pixel value of each of the R pixel, Gpixel, and B pixel at each pixel position may be calculated.

In the embodiment, the hardware structure of the processing unitsincluded in the processor device 16, such as the image acquisition unit53, the brightness information calculation unit 54, the DSP 56, thenoise removal unit 58, the image processing unit 60, the parameterswitching unit 62, and the display control unit 64 is various processorsas follows. The various processors include a central processing unit(CPU) that is a general-purpose processor that functions as variousprocessing units by executing software (program), a programmable logicdevice (PLD) that is a processor whose circuit configuration can bechanged after manufacture, such as field programmable gate array (FPGA),a dedicated electrical circuit that is a processor having a circuitconfiguration designed exclusively for executing various types ofprocessing, and the like.

One processing unit may be configured by one of various processors, ormay be configured by a combination of two or more processors of the sametype or different types (for example, a combination of a plurality ofFPGAs or a combination of a CPU and an FPGA). In addition, a pluralityof processing units may be configured by one processor. As an example ofconfiguring a plurality of processing units by one processor, first, asrepresented by a computer, such as a client or a server, there is a formin which one processor is configured by a combination of one or moreCPUs and software and this processor functions as a plurality ofprocessing units. Second, as represented by a system on chip (SoC) orthe like, there is a form of using a processor for realizing thefunction of the entire system including a plurality of processing unitswith one integrated circuit (IC) chip. Thus, various processing unitsare configured by using one or more of the above-described variousprocessors as hardware structures.

More specifically, the hardware structure of these various processors isan electrical circuit (circuitry) in the form of a combination ofcircuit elements, such as semiconductor elements.

In the embodiment, the invention is applied to the endoscope system thatperforms processing on the endoscopic image as one of the medicalimages. However, the invention can also be applied to a medical imageprocessing system that processes medical images other than theendoscopic image.

EXPLANATION OF REFERENCES

-   -   10: endoscope system    -   12: endoscope    -   12 a: insertion part    -   12 b: operation part    -   12 c: bendable portion    -   12 d: distal end portion    -   12 e: angle knob    -   13 a: mode switching SW    -   13 b: still image acquisition instruction part    -   14: light source device    -   16: processor device    -   18: monitor    -   19: user interface    -   20: light source unit    -   20 a: violet light emitting diode (V-LED)    -   20 b: blue light emitting diode (B-LED)    -   20 c: green light emitting diode (G-LED)    -   20 d: red light emitting diode (R-LED)    -   21: light source control unit    -   23: optical path coupling unit    -   30 a: illumination optical system    -   30 b: imaging optical system    -   41: light guide    -   45: illumination lens    -   46: objective lens    -   48: image sensor    -   50: CDS/AGC circuit    -   52: A/D converter    -   53: image acquisition unit    -   54: brightness information calculation unit    -   56: digital signal processor (DSP)    -   56 a: demosaicing processing unit    -   58: noise removal unit    -   60: image processing unit    -   62: parameter switching unit    -   64: display control unit    -   80: image signal    -   82: first smoothing filter    -   84: second smoothing filter    -   86: third smoothing filter

What is claimed is:
 1. A medical image processing system comprising: alight source unit that emits specific narrow-band light of a shortwavelength; an image sensor that images an observation targetilluminated with the specific narrow-band light, the image sensorincluding a first pixel group including a first pixel and a second pixelgroup including at least a second pixel; and a light source controlcircuit that controls a light emission amount of the specificnarrow-band light, wherein the first pixel has a higher sensitivity tothe specific narrow-band light than the second pixel, the second pixelhas a sensitivity to first long-wavelength light of a longer wavelengththan the specific narrow-band light and the specific narrow-band light,and the light source control circuit controls the light emission amountof the specific narrow-band light on the basis of a pixel value of thefirst pixel obtained in the first pixel and a pixel value of the secondpixel obtained in the second pixel.
 2. The medical image processingsystem according to claim 1, wherein the second pixel group includes athird pixel having a sensitivity to broadband illumination lightincluding the specific narrow-band light and the first long-wavelengthlight, and the light source control circuit controls the light emissionamount of the specific narrow-band light on the basis of a pixel valueof the third pixel in addition to the pixel value of the first pixel andthe pixel value of the second pixel.
 3. The medical image processingsystem according to claim 1, wherein the second pixel group includes afourth pixel having a sensitivity to second long-wavelength light of alonger wavelength than the first long-wavelength light and the specificnarrow-band light, and the light source control circuit controls thelight emission amount of the specific narrow-band light on the basis ofa pixel value of the fourth pixel in addition to the pixel value of thefirst pixel and the pixel value of the second pixel.
 4. The medicalimage processing system according to claim 1, further comprising: aprocessor configured to calculate brightness information indicatingbrightness of the observation target on the basis of the pixel value ofthe first pixel multiplied by a brightness adjustment coefficient forthe first pixel and the pixel value of the second pixel multiplied by abrightness adjustment coefficient for the second pixel, wherein thelight source control circuit controls the light emission amount of thespecific narrow-band light on the basis of the brightness information,and a ratio between the brightness adjustment coefficient for the firstpixel and the brightness adjustment coefficient for the second pixel isdetermined on the basis of a short-wavelength sensitivity toshort-wavelength light including the specific narrow-band light in thesensitivity of the first pixel and the short-wavelength sensitivity ofthe second pixel.
 5. The medical image processing system according toclaim 4, wherein the short-wavelength sensitivity of the second pixel is10% or more of a maximum sensitivity of the second pixel, or 10% or moreof the short-wavelength sensitivity of the first pixel.
 6. The medicalimage processing system according to claim 4, wherein theshort-wavelength sensitivity of the second pixel is 35% or less of amaximum sensitivity of the second pixel, or 35% or less of theshort-wavelength sensitivity of the first pixel.
 7. The medical imageprocessing system according to claim 2, further comprising: a processorconfigured to calculate brightness information indicating brightness ofthe observation target on the basis of the pixel value of the firstpixel multiplied by a brightness adjustment coefficient for the firstpixel, the pixel value of the second pixel multiplied by a brightnessadjustment coefficient for the second pixel, and the pixel value of thethird pixel multiplied by a brightness adjustment coefficient for thethird pixel, wherein the light source control circuit controls the lightemission amount of the specific narrow-band light on the basis of thebrightness information, and a ratio between the brightness adjustmentcoefficient for the first pixel, the brightness adjustment coefficientfor the second pixel, and the brightness adjustment coefficient for thethird pixel is determined on the basis of a short-wavelength sensitivityto short-wavelength light including the specific narrow-band light inthe sensitivity of the first pixel, the short-wavelength sensitivity ofthe second pixel, and the short-wavelength sensitivity of the thirdpixel.
 8. The medical image processing system according to claim 3,further comprising: a processor configured to calculates brightnessinformation indicating brightness of the observation target on the basisof the pixel value of the first pixel multiplied by a brightnessadjustment coefficient for the first pixel, the pixel value of thesecond pixel multiplied by a brightness adjustment coefficient for thesecond pixel, and the pixel value of the fourth pixel multiplied by abrightness adjustment coefficient for the fourth pixel, wherein thelight source control circuit controls the light emission amount of thespecific narrow-band light on the basis of the brightness information,and a ratio between the brightness adjustment coefficient for the firstpixel, the brightness adjustment coefficient for the second pixel, andthe brightness adjustment coefficient for the fourth pixel is determinedon the basis of a short-wavelength sensitivity to short-wavelength lightincluding the specific narrow-band light in the sensitivity of the firstpixel, the short-wavelength sensitivity of the second pixel, and theshort-wavelength sensitivity of the fourth pixel.
 9. The medical imageprocessing system according to claim 1, wherein the number of pixels ofthe second pixel group is greater than the number of pixels of the firstpixel group.
 10. The medical image processing system according to claim2, wherein the number of pixels of the second pixel group is greaterthan the number of pixels of the first pixel group.
 11. The medicalimage processing system according to claim 3, wherein the number ofpixels of the second pixel group is greater than the number of pixels ofthe first pixel group.
 12. The medical image processing system accordingto claim 4, wherein the number of pixels of the second pixel group isgreater than the number of pixels of the first pixel group.
 13. Themedical image processing system according to claim 5, wherein the numberof pixels of the second pixel group is greater than the number of pixelsof the first pixel group.
 14. The medical image processing systemaccording to claim 6, wherein the number of pixels of the second pixelgroup is greater than the number of pixels of the first pixel group. 15.The medical image processing system according to claim 1, wherein acenter wavelength of the specific narrow-band light is included in arange of 400 nm to 450 nm, and a half-width of the specific narrow-bandlight is 40 nm or less.
 16. The medical image processing systemaccording to claim 2, wherein a center wavelength of the specificnarrow-band light is included in a range of 400 nm to 450 nm, and ahalf-width of the specific narrow-band light is 40 nm or less.
 17. Themedical image processing system according to claim 3, wherein a centerwavelength of the specific narrow-band light is included in a range of400 nm to 450 nm, and a half-width of the specific narrow-band light is40 nm or less.
 18. The medical image processing system according toclaim 4, wherein a center wavelength of the specific narrow-band lightis included in a range of 400 nm to 450 nm, and a half-width of thespecific narrow-band light is 40 nm or less.
 19. The medical imageprocessing system according to claim 5, wherein a center wavelength ofthe specific narrow-band light is included in a range of 400 nm to 450nm, and a half-width of the specific narrow-band light is 40 nm or less.20. The medical image processing system according to claim 6, wherein acenter wavelength of the specific narrow-band light is included in arange of 400 nm to 450 nm, and a half-width of the specific narrow-bandlight is 40 nm or less.